This invention relates generally to vehicle headlamps utilizing an enclosed curved reflector member in combination with a hermetically sealed light source to provide improved forward illumination and more particularly to providing combined light and heat shield means in such headlamp assembly so as to avoid light reduction in the projected light beam pattern attributable to the shielding means itself.
Federal highway standards regulate the optical performance of vehicle headlamps to a considerable degree. Such regulations further dictate size, shape and placement of headlamps while still permitting both circular and rectangular headlamp configurations to be employed. Maximum glare from the headlamps above the principal or longitudinal lamp axis is specified and with glare proving further objectionable to the vehicle driver in adverse weather conditions where backscatter impedes visibility, e.g. rain, fog and snow. That providing glare reduction in headlamps being used for forward vehicle illumination represents a long recognized and serious consideration can be appreciated from the number of early issued U.S. Pat. Nos. including, 2,277,563; 2,366,292; 2,858,467; 2,880,347; 2,987,643; and 3,136,914 wherein a filament shield has been provided. In these early headlamp configurations, the reflector and lens member were commonly hermetically sealed together so that one or more bare refractory metal filaments could be therein housed to provide the light source and with the filament shield member simply preventing the direct filament light from going directly to the lens.
In a more recently issued U.S. Pat. No. 4,029,985, assigned to the assignee of the present invention, there is disclosed an improved light shield member for the above type headlamp constructions. The disclosed filament shield for a rectangular headlamp blocks the direct filament light from selected portions of the reflector member. Such an objective is achieved with the filament shield comprising a first surface having a cross section which is geometrically similar to the shape of the lens. Attached to the sides of the shield are tabs having shapes geometrically similar to the respective side wall adjacent to each tab and aligned with respect to the lamp filament to prevent direct light from impinging on the side walls. This shield member is located between the filament and the lens member with a front opening being provided so that direct light from the filament light source reaches the lens. In permitting the forward illumination to include direct filament light, there is likelihood for some of this light to be directed to glare zones in the projected light beam pattern. The glare zones are typically areas of the projected light beam above the horizontal in a representative horizontally aimed beam. Light levels in these glare zones are limited to very low levels, typically 75 candles to 350 candles. Direct filament light may add from 200 candles to 400 candles depending upon the light source brightness and wattage and the orientation of the filament. It becomes desirable for glare reduction, therefore, to provide shielding means for the light source which intercepts direct light from reaching the lens member.
The recent emergence of vehicle headlamps either formed with synthetic organic polymer materials or employing an adhesive sealing together of the lens and reflector members formed with glass introduces a still further serious consideration for proper lamp design. As earlier recognized for such plastic type vehicle headlamps in U.S. Pat. Nos. 4,210,841 and 4,280,173, both assigned to the present assignee, a heat shield member is provided in the lamp assembly. In said rectangular type headlamp construction, such heat shield member is typically located between the light source and the top reflector truncating wall. Its purpose is to intercept and diffuse direct infrared radiation and the convected hot radiation so as to avoid failure under lamp operating conditions. Typical lamp operating conditions leading to such failure include automotive alternator voltages in excess of design (e.g. lamp wattage output), static burning (e.g. reduced heat loss through forced convection) and tight enclosures (limiting natural convective heat loss). In the case of such plastic reflector materials, failure may constitute softening, darkening or outgassing. Adhesive sealing polymers typically fail through outgassing or loss of seal integrity. The heat shield member is designed and placed within the headlamp assembly so as to limit the maximum temperature on the reflector wall or adhesive under the expected operating conditions.
A still further commonly assigned U.S. Pat. No. 4,754,373 discloses an improved vehicle headlamp for developing forward illumination and having reduced dimensions relative to the above identified prior art headlamps. This headlamp comprises an enclosed concave parabolic reflector of a rectangular cross section type and having a single tungsten-halogen light source coaxially located within the enclosed reflector. The headlamp has a glare shield arranged around the light source when such headlamp is utilized for low beam application whereas a different heat shield located above the light source is substituted for high beam applications. More particularly, for the low beam application the glare shield substantially prevents the light emitted by the filament which does not encounter any parabolic portions of the reflector from otherwise escaping through the lens in an uncontrolled manner. Such glare shield is a thin metal member which substantially eliminates any direct filament images from being transmitted by the headlamp. On the other hand, for high beam applications such type glare shield is replaced with a heat shield construction of the type disclosed in the aforementioned U.S. Pat. No. 4,210,841 to simply reduce convected heat within the headlamp. As further disclosed in said prior art reference, the particular glare shield configuration therein employed is physically dimensioned so that the rearward portion of the filament light source protrudes therefrom. Such shielding means thereby enables some direct light from the filament source to reach the top and sidewalls of the reflector member which can contribute to glare. On the other hand, since this general headlamp configuration can also be modified in accordance with the present invention, said prior art patent is also specifically incorporated herein by reference.
It remains desirable, therefore, to provide a glare shield means for vehicle headlamp applications providing still better illumination characteristics. In doing so, it becomes important that the projected light beam pattern avoid shadowing by the glare shield means itself. It remains equally desirable to do so in a manner contributing to other improved operational characteristics in the type headlamps being employed. In such latter regard, many new headlamp products are being designed in an adhesive seal format. Use of halogen source lamps for the light source has obviated the need for perfectly hermetic reflector, lens and adhesive materials. Many of these headlamps are also being designed for smaller size. This trend is evident in the automotive industry in such products as the 150 millimeter width headlamp design. As lamp size is reduced, wattage may be increased to make up for the reduced reflector area. The combination of higher wattage and reduced surface area from which heat may be removed, result in higher internal lamp temperatures. It is this higher temperature of lamp operation which dictates material selection for the newer generation of headlamps. Polymeric materials used for lamp reflectors, lens or joining adhesives must withstand the operating temperature for the design life of the lamp. Materials which are capable of performing in hotter environments, tend to be more costly, or even worse, commonly unavailable. In either case the utility of the headlamp product is reduced or obviated.
It is a principal object of the present invention, therefore, to provide a unitary glare and heat shield means for vehicle headlamp applications having a novel physical configuration.
It is another important object of the invention to provide composite glare and heat shield means for a vehicle headlamp exhibiting improved optical performance.
Still another important object of the present invention is to provide vehicle headlamp construction exhibiting improved glare reduction attributable to the light source shielding means therein employed.
A still further important object of the present invention is to combine the glare and heat shield means for a vehicle headlamp in a manner not requiring substantial modification of the overall lamp construction.
These and other objects of the present invention will become more apparent upon consideration of the following description for the present invention.